Acid phosphate (meth)acrylic monomers, that is compounds with acrylate or methacrylate functionality and ##STR2## functionality have recently become known as adhesion promoting additives for curable acrylic monomer adhesives and coatings. Such compounds have been observed to improve adhesion in formulations for bonding dental and bone materials as well as a variety of metals. They are especially useful on metals such as zinc and aluminum which give poor results with other adhesion promoters such as acrylic acid and acrylic ester acids like those disclosed in U.S. Pat. Nos. 4,431,787 and 4,048,259.
References which describe such acid phosphate monomers and compositions thereof include U.S. Pat. Nos. 3,754,972; 3,987,127; 4,044,044; 4,250,007; 4,223,115; 4,293,665; 4,322,509; 4,452,944; 4,433,124; 4,434,278; 4,259,117; 4,368,043; 4,499,251; 4,525,493; and 4,515,930. Other such references include Jpn Kokai No. 57/167364 (1982); Jpn Kokai No. 49/20238 (1974); Jpn Kokai No. 49/84694 (1984), see Chem. Abst, 101: 153164k; Jpn Kokai No. 56/100803 (1981), see Chem/ Abst, 95: 221461q; and European patents Nos. EP0058483 and EP0074708.
Phosphate compounds, however, have long been known as stabilizers for acrylic monomer compositions and it has been observed that acid phosphate monomers do have a cure inhibiting or slowing effect on compositions to which they are added. See e.g. U.S. Pat. No. 4,322,509.
In Jpn Kokai No. 78/113843 (1978) there are described dental adhesive compositions which employ partially neutralized phosphate monomers in which about 30-90% of the phosphoric acid groups are converted to metal, ammonium or amine salts. Suggested for improved adhesion are the partial salts of "alkali earth metals as magnesium, calcium, and barium, elements which belong to the copper and zinc families, such transition elements as titanium, vanadium, chromium, manganese, iron, cobalt, nickel and zirconium." The only examples, however, are calcium salts. This reference teaches that adhesion improvement decreases after 50% of the phosphoric acid groups are neutralized and falls of considerably when more than 90% of the acid groups are neutralized.
In U.S. Pat. No. 4,446,246 there are described two-part acrylic monomer adhesive compositions, one part of which includes an acrylic monomer/oligomer base and a Cu(I) complex. One such complex is said to be prepared from CuCl.sub.2.2H.sub.2 O and bis(methacryloxy ethyl) phosphate.
Solutions of transition metal salts, particularly copper salts of organic acids in organic solvents have frequently been used as primer accelerators for curable acrylic monomer compositions, particularly anaerobic curing adhesives or sealants. However, the use of such primers frequently results in significant reductions in ultimate cure strength. Nevertheless, because of their advantages in accelerating cure and because, on some substrates, cure of anaerobic compositions cannot be obtained without addition of transition metal salt ion, such primers are widely used.
While the acid phosphate monomers have achieved wide investigation in the art as evidence by the foregoing discussion, such compounds have found only limited application in room temperature curing anaerobic acrylic compositions because of their substantial cure inhibiting effects.